Identity Synchronization for Windows synchronizes significant and creation user attributes, as follows:
Creation attributes. Synchronized between Directory Server and Windows directories whenever a new user is created, according to specified object creation synchronization settings.
Mandatory creation attributes are attributes that are considered “mandatory” to successfully complete a creation action in the target directory. For example, Active Directory expects that both cn and samaccountname have valid values upon creation. On the Directory Server side, if you are configuring inetorgperson of a user object class, Identity Synchronization for Windows will expect cn and sn as mandatory attributes for a creation.
A creation attribute default updates the target directory creation attribute with a default value only when there is no value in the attribute propagated from the originating directory. (Creation attribute defaults can be based on other attribute values. See Parameterized Attribute Default Values)
Significant attributes are automatically synchronized as creation attributes but not the other way around. Creation attributes are only synchronized during user creations.